In addition, there are stark differences for acute LD50 doses among genera, where minute amounts of brodifacoum bait caused death in domestic canids but domestic felids required doses 5 to 40 times higher . The same variability seen in both mustelids and other carnivores suggests that predicting clinical thresholds for fishers would be pre-mature. Furthermore, AR exposed fishers had an average of 1.6 AR types within their systems, and possible interaction effects from a combination of 2 or more AR compounds within a fisher and other species are entirely unknown.Spatial analyses did not reveal any obvious point sources of AR exposure. Instead, these analyses suggested that exposure is widespread across the landscape. Previous studies expected that exposure to AR compounds would be clustered near areas of human activity or in habitations and that exposure would not be common outside of these areas. Incongruously, data from this study refuted this hypothesis thus making the finding even more significant. Furthermore, these exposures occurred within a species that is not closely affiliated with urban, peri-urban or agricultural settings in which second-generation ARs typically are. Before the June 2011 Environmental Protection Agency regulations, second generation class ARs could be purchased at local retailers, vertical farming system with recommendations for placement in weather- and tamperresistant bait containers no more than 50 feet from any building. However, since June 2011, second generation ARs have not been available to consumers at retail, but only at agricultural stores with additional form and weight restrictions.

These newly passed regulations are aimed at further restriction of irresponsible and illegal use of ARs. However, we would have expected that with either pre- or post-June 2011 regulations, second generation AR exposed fishers would have overlapped with urban, peri-urban, or agricultural environments. This pattern is acknowledged in several studies, such as Riley et al. where bobcat and mountain lion total quantification levels of AR exposure were associated with human-developed areas. Numerous studies have documented that secondary poisoning cases are closely associated with recent agricultural or urban pest eradication efforts. The majority of habitat that fishers in California and fishers throughout the DPS currently and historically occupied is not within or near agricultural or urban settings. Several fishers that were exposed had been monitored their entire lives and inhabited public or community lands where human structures are rare or non-existent . Therefore, exposure from first or second generation AR use at or within 50 feet of residential or agricultural structures and settings were considered unlikely due to fisher habitat requirements and general lack of association with humans. This suggests that wide-spread non-regulated use of second generation second generation ARs is occurring within the range of fishers in California, especially on public lands. A likely source of AR exposure to fishers is the emerging spread of illegal marijuana cultivation within California public and private lands. In 2008 in California alone, over 3.6 million outdoor marijuana plants were removed from federal and state public lands, including state and national parks, with thousands of pounds of both pesticides and insecticides found at grow sites. In 2011, a three week eradication operation of marijuana cultivation removed over 630,000 plants and 23,316 kg of trash including 68 kg of pesticides within the Mendocino National Forest in the northern California fisher populations range. Anticoagulant rodenticides and pesticides are typically dispersed around young marijuana plants to deter herbivory, but significant amounts of AR compounds are also placed along plastic irrigation lines used to draw water from in order to deter rodent chewing .

A recent example in which over 2,000 marijuana plants were removed less than 12 km from one of the project areas revealed that plants on the peripheraledges as well as nearby irrigation had large amounts of second generation AR placed . Finally, just within a single eradication effort, multiple kilometers of irrigation line within National Parks and Forests in California were removed. Placement of ARs at the grow sites and along irrigation lines which jut out great distances from the grow site itself may explain why there are no defined clusters of AR exposure. It is noteworthy that the AR fisher mortalities we documented occurred in different areas of their California range but within a relatively short seasonal period between mid-April to mid-May. We cannot specify the exact explanation or source contributing to all AR mortalities that occurred within this short temporal period. This period is when females are providing for offspring as well as males searching for mates; however, preliminary spatial data for fishers in California document that females have more confined home-ranges during this period, while males have slightly larger home-ranges . Additionally, several books available to the general public identify the optimal time for planting marijuana outdoors is during mid to late spring, and seedlings are especially vulnerable to rodent pests . Of additional concern is that April to May is the denning period for female fishers and a time when fisher kits are entirely dependent on their mothers. The documentation of a lactating female mortality attributed to AR toxicosis during this period suggests that most likely kits would be abandoned and die from female mortalities during this time. In conclusion, this study has demonstrated that fishers in the western DPS, which are of conservation concern and a candidate for protection under the Endangered Species Act, are not only being exposed to ARs, but ARs are a direct cause of mortality and indirect mortality in both of California’s isolated populations. Consequently, these toxicants may not only pose a mortality risk to fishers but could also pose significant indirect risks by depleting rodent prey populations upon which fishers depend.

The lack of spatial clustering of exposed individuals suggests that AR contamination is widespread within this species’ range and illegal or irresponsible use of ARs continues despite recent regulatory changes regarding their use. Because we do not know the long term ecological ramifications of these toxicants left on site long after marijuana grows are dismantled, heightened efforts should be focused on the removal of these toxicants at these and adjacent areas at the time of dismantling. Further regulation restricting the use of ARs to only pest management professionals as well as continued public outreach through state wide Integrated Pest Management programs may be warranted. In addition, promotion of compounds that do not possess the propensity for secondary poisoning should be considered in non-professional use settings. Furthermore, ARs in these habitats may pose equally grave risks to other rare and isolated California carnivores such as the Sierra Nevada red fox , American marten , wolverine , gray wolf or raptors such as northern spotted owls , California spotted owls and great gray owls . Future research should be directed to investigating potential risks to prey populations as well as other sympatric species that may allow a better understanding of the potential AR sources contributing to these exposure and mortality rates from anticoagulant rodenticides.Edge detection is the first step of human visual perception and is fundamentally important in the human visual system . Edge detection significantly reduces the amount of data to be processed, vertical farming racks since it extracts meaningful information and preserves important geometric features. To detect the edges of an object, the object information is processed by either digital computation or analog computation. In practice, as an optical analog computation element, spatial differentiator enables massively parallel processing of edge detection from an entire image, which offers advantages over digital computation: It can deal with realtime and continuous image processing with high speed and is power-saving in specialized computational tasks . During the past few years, optical meta materials and meta surfaces have been suggested to perform analog spatial differentiation for edge detection which show superior integration capability compared with the traditional bulky system comprising lenses and spatial filters . A suitably designed meta material structure was theoretically proposed to perform desired mathematical operations including edge detection as light propagates through it . Deliberately designed layered structure was also suggested for spatial differentiation when an incident beam is reflected from it . Plasmonic dark-field microscopy utilizes near-field surface plasmon waves to excite the object, and can be also treated as an efficient approach for edge detection . However, to the best of our knowledge, free space broadband edge detection has not been reported yet because either the system can only be applied for surface imaging or the fabrication involved is too complicated . Here, we propose a mechanism to implement an optical spatial differentiator consisting of a designed Pancharatnam–Berry -phase meta surface inserted between two orthogonally aligned linear polarizers . Unlike other spatial differentiator approaches, our method does not depend on complex layered structures or critical plasmonic coupling condition, but instead is based on spin-to-orbit interactions. Experiment confirms that broadband optical analog computing enables the edge detection of an object and achieves tunable resolution at the resultant edges. Furthermore, meta surface orientation-dependent edge detection is also demonstrated experimentally.As shown in Fig. 2A, the sample is made of form-birefringent nanostructured glass slabs. The diameter of the glass substrate is 2.5 cm, the thickness is 3 mm, and the pattern area of the sample is 8 mm by 8 mm. The meta surface pattern is fabricated by a femtosecond pulse laser inside of glass, 50 μm beneath the surface. Under intense laser irradiation, a plasma of high free electron density is generated by a multi-photon ionization process. The interference between the plasma and the incident light beam leads to the stripe-like nanostructure as reported . By carefully controlling the polarization of incident beam, the desired orientation of the nanostructure, which is perpendicular to this polarization, can be obtained. More fabrication details could be found in our previous work . We utilized the polariscopy method to demonstrate the local optical slow-axis orientation of this birefringent structure .

As shown in Fig. 2B, crossed linear polarizer imaging under 80× magnification emphasizes the transverse gradient pattern of the optical axis, which corresponds to the dotted square area in Fig. 2A. We can clearly see the local orientation of the microscopic structures, i.e., the slow-axis distribution φðx,yÞ of laser-induced form birefringence. The red bars indicate the orientation of the slow axis over one period of this sample. The nanostructures are on the order of 30∼100 nm, as indicated from the scanning electron microscope image in Fig. 2B, Inset. The structure dimension is much smaller than the working wavelength, therefore we can treat it as a birefringence medium with spatially variant optical slow axis. When the light beam passes through the designed inhomogeneous birefringent medium with locally varying optical axis orientations and homogeneous retardation, it will acquire a spatially varying PB phase .The first lens yields the Fourier transform of the object at its back focal plane, which is exactly the position of the meta surface. In turn, the second lens performs another Fourier transform, delivering a duplicate of the object. When the light passes through the 4f system, we obtain two vertically shifted LCP and RCP images with overlapping area being linear-polarized as shown in Fig. 3 A–C. The amount of shift of the two images is difficult to see due to the small phase gradient of the meta surface. To block the overlapping area while preserving circularly polarized edge, we put an analyzer after the meta surface so that only the edges can go through, as displayed in Fig. 3 D–F. The wavelengths are chosen as 430, 500, and 670 nm, which not only confirms the proposed concept of edge detection, but also demonstrates its broadband capability. The broadband property of our meta surface originates from the geometric phase of the nanostructure orientation, which is intrinsically independent of wavelength . Additionally, the transfer function of the whole edgedetection system is experimentally measured and provided in SI Appendix, Fig. S3, which shows a typical response for the edgedetection function . Additionally, we demonstrate the tunable resolution of the edge images corresponding to different PB phase gradient period Λ. For this experiment, we choose the UCSD Triton insignia as our object . Fig. 4 A–D shows the photos of four meta surfaces with Λ equal to 500, 750, 1,000, and 8,000 μm. Fig. 4 E–H corresponds to the polariscope optical image of the meta surfaces of the first row, which shows different numbers of period within the same field of view .